Industrial process control systems are widely applied in industrial plants, factories, and other field sites where they are used to coordinate and automate multiple operations such as sensing, monitoring, communication and device actuation. In these control systems, control devices both control and monitor spatially distributed field devices such as sensors, valves, and switches by communicating messages and data with these devices over specialized fieldbus networks using communication protocols particular to each type of fieldbus network. Within a given fieldbus network, the control devices and the field devices are typically configured to communicate with and respond to a single fieldbus protocol corresponding to the particular network.
The control devices may be implemented as microprocessor-based controllers, computers or workstations that control processes by communicating control commands to the fieldbus devices. The control commands may be implemented as software, and can be adapted or modified without affecting any of the hardware of the process control system. For example, a process engineer working from a workstation computer might develop a program routine that causes a control device to request a measurement of a fluid level at a level sensor field device, compare the measured level with a pre-defined threshold level, and then actuate a feed valve based on whether the measured level is above or below the pre-defined threshold. The threshold level may be pre-set or modified by the process engineer through a software application running on the workstation. To accomplish this high level of control and flexibility, it is crucial that software commands at the workstation be correctly adapted for the appropriate fieldbus network and protocol to which the control device and level sensor are coupled.
Currently, there are three predominant fieldbus network platforms: Foundation fieldbus, Profibus and the Hart network. Historically, each of these fieldbus network platforms was developed at slightly different times and designed for somewhat different functionality. Consequently, extensive investment and infrastructure has been allocated to each of the three dominant platforms, with the result that many process control systems and industrial sites include a combination of fieldbus network platforms. While each of the fieldbus networks generally use twisted-pair cables, their respective physical layers are not identical, and their respective transaction mechanisms (e.g., master/slave, multi-master/multi-slave) are quite distinct from one another. To integrate control operations at such a site, the control devices need to be able to interface with and communicate over the various pre-installed fieldbus networks at the site using the appropriate protocol.
While there are several single-network interfaces available which allow an operator to connect a control device to a Foundation Fieldbus network or a Profibus network, for example, using a Serial bus or a PCMCIA connection, such interfaces do not offer the ability to adaptively change connectivity between different fieldbus platforms. Accordingly, when an operator wishes to access different fieldbus networks, the interface must be manually switched. Protocol gateways or mapping devices have also been proposed, which translate messages from one protocol or device description language into another. For example, U.S. Pat. No. 5,923,557 to Eidson describes a mapper device that translates instructions from an application program into multiple fieldbus protocols at a fieldbus network interface. However, in the system described, a separate mapper is required for each of the multiple fieldbus networks to which an interface is desired, making this a somewhat cumbersome solution for generalized access to fieldbus networks.
What is therefore needed is a single standard interface that can be used to provide access to the most prevalent existing fieldbus networks from any common workstation, server, personal digital assistant, programmable controller, or similar microprocessor-based control device.